Method and apparatus for inductive heating

ABSTRACT

Method and apparatus for exercising effective electromagnetic influence across an entire planar surface of an electrically conductive object to inductively heat the planar surface when the dimensions of the planar surface exceed the effective limits of a field provided by opposite runs of an inductive heating coil. The method and apparatus is particularly applicable to sealing widemouth containers by bonding across and to the container finish a closure member. An assembly of the closure member, thermoplastic bonding material and the container finish is conveyed in a linear direction past the novel inductive heating coil. The heating coil acts to shift the effective magnetic influence of the coil across the path without physically moving the coil. Novel structures of inductive heating coils are also disclosed.

I United States Patent Kennedy [54] METHOD AND APPARATUS FOR INDUCTIVEHEATING [72] Inventor: Leo J. Kennedy, Toledo, Ohio [73] Assignee:Owens-Illinois, Inc.

[22] Filed: Feb. 1, 1971 21 Appl. No.: 111,479

1451 Sept. 26, 1972 Primary Examiner-J. V. Truhe Assistant ExaminerHughD. Jaeger A!t0mey-Philip M. Rice and E. J. Holler [57] ABSTRACT Methodand apparatus for exercising effective electromagnetic influence acrossan entire planar surface of an electrically conductive object toinductively heat the planar surface when the dimensions of the planarsurface exceed the effective limits of a field provided by opposite runsof an inductive heating coil. The method and apparatus is particularlyapplicable to sealing wide-mouth containers by bonding across and to thecontainer finish a closure member. An assembly of the closure member,thermoplastic bonding material and the container finish is conveyed in alinear direction past the novel inductive heating coil. The heating coilacts to shift the effective magnetic influence of the coil across thepath without physically moving the coil. Novel structures of inductiveheating coils arealso disclosed.

19 Claims, 8 Drawing Figures 'PATiNTEnsirzs I972 3.6 94.609

sum 1 or 2 3O HEATING/ CURRENT SOURCE INVENTOR LEO J. KENNEDY ATTORNEYPATENTEDSEPZB 1912 3,694,609

' SHEET 2 [1F 2 INVENTOR LEO J. KENNEDY ATTORNEY METHOD AND APPARATUSFORINDUCTIVE I HEATING BACKGROUND OF THE INVENTION In packaging or bottlingmaterials it is frequently desirable to effect positive hermetic sealingof the receptacle or container. Such scaling is particularly required incases where the packaged material deteriorates upon exposure to air ormoisture, or is of a corrosive, toxic, flammable or explosive nature.

In the past a hermetic seal was attempted by the crimping of metal foilsto metallic-tins or cans but this method had disadvantages in fillingand the seal was not always perfectly hermetic. Closure caps with waxedvpulpboard pads or wads were tried :to which were lightly heat-sealeddouble glassine membranes. The pads were first made adhesive by passingthem under glue-coated rollers. The caps were then applied to thecontainers and after the adhesive has had time to dry out, the caps'wereunscrewed and the'membranes part fromthe waxed pads and remain adheredto the finishes of the containers. In this instance the adhesive takessome time to dry and during this period water vapor is absorbed bythecontents of the container. Moreover it wasdifflcult for the efficiencyof the operation to be, inspected at the end of the packing line. Morerecently sealing has been effected by completely fusing a thermoplasticmembrane to a container of thermoplastic material by an inductiveheating method, as disclosed inU. S.v Pat. No. 2,937,481. In mostinstances this sealing method is too drastic since theseal cannot bebroken without damaging or distorting the container neck and thus makesre-sealing or reuse difficult.

The membrane sealing process has been further refined so that a processfor applying a sealing membrane to a container has beendeveloped whereineither the membrane or the container or both is of metal. This method isdisclosed in U. S. Pat. No. 3,460,310. The membrane is placed undersealing pressure onto the container finish and the metal of the membraneor container finish is heated by means of an induced radio frequencycurrent to. a. temperature sufficient to soften a thermoplastic materialcoated on the material of the membrane whereby the membrane is removablyad- To overcome this problem a series of wide-mouth I containers arecontinuously sealed by rotating each hered to the container withoutdistortion of the container.

The last described method of sealing containers is the most satisfactorydeveloped to date. However, the induction heating methods utilizedrequire either a stop-and-go typeof packaging line .or limit the size ofthe container finish being sealed to small mouth containers notexceeding approximately one and one-half inches in diameter. Thesedisadvantages occur because the inductive heating coils presently inownin the art are not able to exercise effective electromagnetic influenceon the entire planar surface of a metallic foil membrane when themembranes are moved continuously past the inductive heating coil whenthey exceed approximately one and one-half inches in diameter. This istrue because whenthe opposite sides or runs of the inner turns of aninductive heating coil are separated beyond a certain limit the centralportion of a metallic susceptor passing beneath the coil does notreceive effective electromagnetic influence and thus is not heated toactivate the thermoplastic bonding material.

container as it passes beneath an elongated load coil so that the entireperiphery of the container finish is exposed to the effectiveelectromagnetic influence of the coil during the rotation. Rotation offilled containers may disturb or spill the contents, is difficult withflexible plastic containers, introduces more costly equipment formaintenance and is not as fast as desired. Alternatively, astop-and-gomotion is used in which the container is momentarily haltedand a load coil having a .diameter substantially the same as thecontainer finish is moved into inductive .heating relationship therewithto effect the seal. This sharply limits the speed of operation of afilling and packaging line. Accordingly, it is an object of thisinvention to provide an improved method and apparatus for packaging.Another object of this invention is to provide an improved method andapparatus for exercising effective electromagneticinfluence across anentire planar surface of an electrically conductive object toinductively heat the planar-surface when the dimensions of the planarsurface exceed the effective limits of a field pro- .vided by oppositesides of an inductive heating coil when current is flowing therethrough.

It is a still further object of the present invention t provide methodand apparatus for applying membranes, both metallic and non-metallic, towide-mouth containers, also metallic or non-metallic, which will give ahermetic gas-tight seal, and which may be effected on continuouslymoving containers.

SUMMARY OF THE INVENTION Theabove objects are carried outin a preferredembodiment for practicing the invention which features a method ofexercising effective electromagnetic influence across an entire planarsurface of an electrically conductive object by moving the planarsurface of the object in a linear direction to-define a path, andforming an inductive heating coil having at least one elongated turnwhich defines a plane, the elongated turn having a major axis. Theelongated turn is disposed so that the plane defined thereby is aninductive heating relationship with and substantially parallel to themovement of the planar surface along the path, and so that the majoraxis of the elongated turn is substantially parallel with the directionof movement of the planar surface. First and second runs of theelongated turn are extended generally longitudinally respectively alongfirst and second sides of the major axis. The effective magneticinfluence of the first and second runs is shifted across the path bydisposing one portion of each run adjacent the major axis, disposinganother portion of each run adjacent the respective outer edge of thepath, and connecting two portions of each run with a third portionextending obliquely with respect to the major axis. When inductive,heating current is flowed through the coil and the planar surface ismoved through the path adjacent the coil the effective magneticinfluence is shifted transversely across the planar surface as it movesthrough the path to effectively heat the entire planar surface.

Other objects, advantages and features of this invention will becomeapparent when the following description is taken in conjunction with'theaccompanying drawings, in which:

' FIG. 1 is a side elevational view of apparatus embodying the teachingsof this invention; i

FIG. 2 illustrates a wide-mouth container and closure arrangement whichmay be utilized in practicing this invention;

FIG. 3 is a'plan view of a first embodiment of a novel inductive heatingcoil for practicing this invention;

FIG. 3a is a cross-sectional view of an alternate embodiment of the coilillustrated in FIG. 3; and

FIGS. 4, S, 6, and 7 illustrate diagrammatically plan views of otherembodiments of inductive heating coils illustrating the teachingsof'this invention.

DESCRIPTION OF THE PREFERRED v EMBODIMENTS By means of the process ofthis invention, metallic or non-metallic membranes may be applied tometallic or non-metallic containers, provided that either the mem braneor the container is metallic. .Theprocess of the invention may beusedtoapply a metal membrane to a metal container, a glass container, aceramic container,

or a synthetic plastic container. v

finish of the container may have the coating of therfmoplastic bondingmaterial. When the membrane and the finish of-the-containerare heated bythe induced currentffrom the inductive heating, coil the thermoplasticbonding material softens sufficiently toadhere the membrane to thecontainer.

When the metal membrane is applied to a glass or synthetic plasticcontainer, either the membrane or the finish of the container may havethe coating of thermoplas tic bonding material. In the case of asynthetic plastic container, to avoid distortion of the container, thethermoplastic coating must have-a melting point lower than the materialof the'container. By means of the invention'membranes of non-metallicmaterial may be applied to metal'containers. For instance, a papermembrane maybe applied-to a metal container by applying to the membraneor the finish of the container the thermoplastic heat sealing coating.As before, this coating softens sufficiently to adhere the membrane tothe container when the container finish is heated by the induced currenttherein. A thermoplastic membrane may he applied to a metal containerand here it is not absolutely necessary, although it may he sometimesdesirable, to use a coating of thermoplastic adhesive.

Normally, containers provided with sealing membranes are also providedwith closure caps, although this is not always necessary. The closurecaps may also be provided with resilient wads such as pulpboard orcomposition cork wads. Basically there are two types of closure caps foruse for such containers as the present invention involves, and these maybe classified broadly as the snap-on" type and the screw-on type. Thescrew-on type may have a continuous lip for engagement with acorresponding thread on a container neck.

The screw-on type caps may be formed of a metal, synthetictherrnosetting materials, and synthetic thermoplastic materials. Thesnap-on type caps] are normally formed from metal or flexible plasticmaterial, but can be formed of paper.

When a screw-on plastic closure cap is used, the cap may be titted witha resilient wad in the metal foil membrane. The cap may then be screwedonto the container to develop sealing pressure on themembrane or to holdthe membrane and the container finish in sealing contact with thethermoplastic bonding material, after which current will be induced inthe foil membrane. It is possible for the resilient wad and the metalfoil membrane to be formed as a unitary article. A sheet of wad materialmay be stuck to. a sheet of metal foil and then discs may be cut fromthe laminate so formed.

. When a snap-on plastic or paper closure cap is used, the cap and themembrane maybe all applied to the container at the same time. Thesealing members may be metallic or non-metallic. Metallic foils ofaluminum or tin make good membranes. Non-metallic membranes may includethose made from paper, glassine, polyethylene and the'like; 1 Thethermoplastic coatingmay be of a resin, a naturalor synthetic wax, asynthetic thermoplastic material such as polyester, or the like. Thethermoplastic material may be coated on the whole of the underside ofthe membrane, or it may be coated in the form of an annular ring onthe-periphery thereof.

Plastic containers to which -membranes may be sealed by means of thepresent invention include any of the synthetic plastic materials, butwhich materials preferably have a higher melting point than the materialused for the thermoplastic bonding coating.

Referring to FIG. 1 there is illustrated acontinuously running conveyor10 for moving a wide-mouth container assembly vl2 in a linear direction32 beneath an inductive heating coil 40 which is connected via terminals 41 to a current source 30. H l i I Referring to" FIG. 2 there isillustrated an exploded view of a container assembly l'2.-A container 14has an upwardly extending finish 16. A laminated disc closure memberpreferably comprises a membrane which includes a thermoplastic bondingmaterial-layer 20 and a metallic foil susceptor layer 22. A supportlayer of kraft paper or synthetic plastic material or the'like may beprovided if the metallic foil susceptor is not of a strength orthickness to properly-retain the contents of the container 14. 'Thesupport layer 24 thus may be made of a material which is sufficientlystrong to enable use of the disc closure member 18 withouta cap such asillustrated at 26.

The cap 26 may be of a screw-on or, preferably, a snap-on type ofclosure which functions to protect the disc closure member 18 and/or tomaintain the thermoplastic bonding layer 20 in sealing contact with thefinish 16 and the susceptor layer 22. Alternatively,

other means may be utilized to maintain the sealing relationship betweenthe disc closure 18 and the finish 16. For example, an endless belt maybe used having a lower run extending beneath the inductive heating coil40 to press downwardly upon disc 18 and a return run which maybedisposed above the inductive heating .coil 40. Such an endless beltwould be made of non-metallic material to prevent interference with theexercise of effective electromagnetic influence therethrough to heat thesusceptor 2 2.

It should also be recognized that although the use of a unitary membraneor disc 18 as described above is preferable, this invention can also bepracticed by utilizing a closure member, a thermoplastic bondingmaterial between the closure member and the container finish, and aseparate metallic susceptor disposed in conductive heating relationshipwith the thermoplastic coating while being passed in inductive heatingrelationship with the coil 40. v

Referring now to FIG. 3 there is illustrated a plan view of theinductive heating coil designated generally at 40. Terminals 41 and theturns of the coil 40 are preferably formed from copper tubing whichcirculates container assembly 12 generally, and in particular of i themetallic susceptor 22, is indicated by the arrows 32. While thedirection of movement in this instance is rectilinear, curvilinearmovement of the container assembly 12 is within the scope of thisinvention, the configuration of the coil 40 being modified accordinglyto accommodate the type of linear movement.

The path of the susceptor 22 is illustrated by showing the outer edges36, 38of'the path; It will benoted that the linear direction 32 of thesusceptor 22 is substantially parallelwith the major axis 42 of the coil40.

j The copper tubing conductor of coil 40 forms at least one elongatedturn which defines a plane for disposition in inductive heatingrelationship adjacent and substantially parallel to the path defined bymovement of the planar susceptor 22 in the linear direction 32. Theelongated turnincludes first and second runs44, 46

' connectedby crossover runs 47. The first and second runs 44, 46 extendgenerally longitudinally along and on first and second sides of themajor axis 42, respectively. v

Each of the first and second-runs 44, 46 has portions 50 positionedsuffi'ciently close to the major axis 42 to permit the exercise ofeffective electromagnetic influence, when current is passingtherethrough, on the path and thus the susceptor 22 when adjacent themajor axis 42. The portions 50 do not exercise effective electromagneticinfluence on the outer edges 36, 38 of the'path nor on the outer edgesof the susceptor 22.

Each of the first and second runs 44, 46 has other portions 48 spacedfrom the major axis 42 to permit the exercise of effectiveelectromagnetic influence, when current is passing therethrough, on therespective outside. edges 36, 38 of the path. The portions 48 do not sthe path 34 and includes at least one excursion obliquely toward andthen away from the major axis, and a second part which extends generallyadjacent the one outside edge. The second run comprises one partopposite the one part of the first run which extends linearly adjacentthe outside edge of the path, and a second part which is opposite to thesecond part of the first run and starts adjacent the other outside edgeand includes at least one excursion obliquely toward and then away fromthe major axis. The first and second runs of the coil 40 each furtherinclude linearly extending sections 50 adjacent the major axis 42connecting the inner reaches of each excursion of the oblique portions52.

When a wide-mouth container fitted with a laminate closure 18 is passedin the direction 32 beneath the coil 50, the portions 48 of the coil 40will effect an electromagnetic influence on the outside edges of thelaminate 18 to activate the thermoplastic material 20 to bond to thefinish 16 of the container. The oblique portions 52 of the coil 40 andthe portions 50 at the inner reaches of the excursions defined by theoblique portions 50 will effectively shift the electromagnetic influencetoward and away from the major axis 42 of the coil 40 to induce currentflow and thus heat in the central portion of the susceptor 22. This heatis conducted to the central portion of the thermoplastic layer 20 toactivate the thermoplastic material to effect a bonding of the remainderof the perimeter of the laminate 18 to the finish of the container 16.

Thus, the shifting of the electromagnetic influence from specific areasof the laminate to other specific areas of the laminate in successionfor the length of the coil provides hermetic sealing of a containerwhile it is in constant linear motion, enabling rapid and effectivesealing of wide-mouth containers.

When alternating electric current flows in a conductor, a symmetricalelectromagnetic field is established around the conductor. If theconductor is formed into a loop or coil, the alternating magnetic fieldis intensified. The actual intensity is determined by the magnitude ofthe current flowing through the coil and the number of turns in thecoil. When more than one turn is utilized in a coil the magnetic fieldis distorted to provide areas of maximum electromagnetic influence.

The resistance offered by the work piece to the flow of the inducedcurrent produces heat in it proportional to the electrical resistivityof the workpiece and to the square of the current flowing. Thus, anymetal part or other conductive material placed adjacent a coil energizedwith alternating electric current heats without physical contact betweenthe part and the coil. The current flowing through the coil and thespacing between the coil and the workpiece determines the amount ofinduced current in the workpiece and thus the amount and location of theheating. Thus the design of a coil with respect to the number of turnsand the magnitude of the current flowing therethrough and the spacing ofthe workpiece are all to be considered when working with inductiveheating. In this instance the design must insure sufficient heat in thesusceptor to conductively activate the thermoplastic bonding materialwithout scorching, melting or otherwise damaging the laminate. Thecharacteristics of the foil and the bonding material are consideredalong with the speed of a container being passed by the coil toeffectively seal a membrane as disclosed to the container finish withoutdamaging the laminate.

The embodiment of the coil illustrated in FIG. 3 has been usedexperimentally to effectively activate a polyester bonding materialtoseal the finish of a polyethylene container to an aluminum foilsusceptor which has a backing of kraft paper. This has been accomplishedwithout scorching or otherwise damaging any portion of the laminate andwhile effecting at hermetic seal on containers having a finish diameterof five inches at conveying speeds which process more than 150containers per minute.

Thus, when a cap 26 is utilized a finished package is provided which hasa tamper proof seal, a hermetic seal, and a re-seal capability.Moreover, the configuration' of the container finish is immaterial withthe method and apparatus disclosed herein. That is, the top of thecontainer finish may be circular as shown,

square, triangular, rectangular, with a pour spout or with other specialpurpose configurations designed into the final shape.

While the'configuration and shape of the inductive heating coilillustrated in FIG. 3 is primarily concerned with laminate closuresealing as hereinbefore described, it is to be recognized that theprinciples disclosed for this method and apparatus can be utilized toeffectivelyand selectively inductively heat the planar surface of anyconductive material being passed adjacent the coil 40.

The coil illustrated in FIG. 3 may be utilized as shown with the maximumelectromagnetic influence of the coil being concentrated adjacent theinside turn of the coil. However, the magnetic field may be furtherdistorted .to shift themaximum area of effective influence and/or todistribute the electromagnetic field. Referring to FIG. 3a there isshown an embodiment in whichv a single turn, metallic sheath secondary.54 is brazed at 56 to the inner turn of the coil 40; The copper barinductor 54 extends around the turns of the coil between the coil andthe path 34. The inductor 54 is insulated from all but the inner turn byair or insulation as indicated'at- 5,8. The copper bar inductor 54 issplit, for example adjacent the input terminals to the coil 40, toprevent the induction of circulating currents therein. The inductor 54distorts the electromagnetic influence of the plurality of turns of thecoil 50 to move the maximum-region of electromagnetic influence moretoward the outside of the coil and to distribute the electromagneticinfluence more evenly, thus permitting a more generalized inductiveheating effect rather than localized in a maximum electromagneticinfluence area.

Referring to FIGS. 4, 5, 6, and 7 there are shown alternate embodimentsof inductive heating coils utilizing the principles disclosed herein andillustrating alternate coil configurations. The coils represented inFIGS. 4 through 7 are diagrammatically illustrated as single turn coilsas viewed from above to show the configurations required with thegreatest clarity. The number of turns in each coil will be determined bythe specific job requirements.

The coil 60 in FIG- 4 has a major axis 62 with a first run 64 and asecon run 6 xtending longitudinally along the major axis. Portions 68 ofthe coil 60 are disposed adjacent the path edge while portions 70 aredisposed adjacent the major axis. Portions 68 and 70 are connected byoblique portions 72 enabling coil 60 to perform the function of shiftingthe electromagnetic [influence with respect to a planar metallic surfacepassing along major axis 62.

The coil 80 of FIG. has a major axis 82 with a first run 84 disposed onone side of the axis 82 and a second run 86 disposed on the other sideof axis 82. Portions 88 are disposed adjacent path edges while portions90 are disposed adjacent the major axis 82. Oblique portions 92 connectportions 88 and to effect a shifting of the electromagnetic influenceacross the path.

The bow-tie or sandglass configuration of FIG. 4 may be utilized toshift the electromagnetic influence over all areas of a container finishtwice to insure sealing. The half sandglass configuration in FIG. 5 maybe utilized when a double sealing effect is not required. Either of theconfigurations of FIGS. 4 and 5 may be utilized when it is desired toinitiate the sealing on the outside edges of a container finish andterminate the sealing on the central portions of the container asit'passes along the path.

In the coils of FIGS. 4 and 5 the first and second runs each startadjacent their outside edge of the path and continue obliquely inwardlytoward each other and the major axis until the major axis is undereffective electromagnetic influence. In the coil of FIG. 4 the first andsecond runs continue from their innermost position obliquely outwardlyaway from each other and the major axis returning to a position adjacenttheir respective outer edge of the path.

Referring to FIG. 6 the coil has a major axis 102 with a first run 104disposed on one side and a second run 106 disposed on the other side.Portions 108 are disposed adjacent the path edge while portions 110 aredisposed adjacent the major axis. Portions 108, 110 are connected byoblique portions 112. The configuration of FIG. 6 may be utilized whenit is desired to initiate sealing of a container finish at the centralportion of the laminate and then sealing the laminate from the centralportion outwardly to the outer edges.

In the coil of FIG. 6 the first and second runs thus each start adjacentthe major axis and continue obliquely outwardly away from each other toa position adjacent their respective outer edges of the path. The firstand second runs then continue from their outermost position obliquelyinwardly toward each other and the major axis until the major axis isunder effective electromagnetic influence.

Referring to FIG. 7 there is illustrated a coil having a major axis 122with a first run 124 disposed on one side and a second run l2 6'disposedon'the other side. Portions 128 are adjacent the path edges whileportions 130 are adjacent the major axis 122. Oblique portions 132connect portions 128 and 130. The corifiguration of FIG. 7'may beutilized to effect a seal in a sweeping motion across the laminate.

In the coil of FIG. 7 one of the first andsecond runs starts adjacentthe major axis and continues obliquely outwardly to a position adjacentits respective outer edge of the path. The other of the first and secondrun starts adjacent its respective outer edge of the path and continuesobliquely inwardly to a position adjacent the major axis.

It is to be recognized that any of the coil configurations illustratedin FIGS. 3 through 6 may be turned end-for-end or that the containersmay be passed adjacent thereto in the opposite linear direction.

In summary, the firstand second runs of the layerlike coils describedherein have conductor portion means positioned to permit electromagneticinductive heating of the edges of the planar path defined by passage ofthe susceptor, and further conductor portion means positioned to permitelectromagnetic inductive heating across the planar path. The latterconductor portion means includes the obliquely extending conductorportions and/or the conductor portions adjacent the major axis of thecoils.

There has thus been disclosed apparatus for sealing wide-mouthcontainers by bonding across and to the container finish a closuremember which includes means for-conveying a container assembly, meansfor supplyinginductive heating current, and an inductive heating coilconnected to the current source and disposed. adjacent the path of thecontainer assembly. The container assembly includes a thermoplasticbonding material held in place between a closure member and thecontainer finish in contacting relationship with both. The containerassembly further includes a planar metallic susceptor disposed inconductive heating relationship with the bonding material so thatcurrent induced in the susceptor will conductively heat the bondingmaterial.

In conclusion, it is pointed out that while the illustrated examplesconstitute preferred and practical embodiments of my invention, 1 do notlimit myself to the exact details shown since modification of thesedetails may be made without departing from the spirit and scope of theinvention. v

lclaim:

1. An inductive heating coil for connection to a source of inductiveheating current for heating a planar surface of a conductive materialcomprising a. a conductor shaped into a plurality of elongated turnsforming a layer coil, one side of said layer defining a plane fordisposition in inductive heating relationship adjacent and substantiallyparallel to a planar path defined by movement of a planar surface in alinear direction, I

b. the elongated turns of said layer having a major axis for dispositionsubstantially parallel to the linear direction of movement of the planarsurface in defining said planar path,

c. said elongated turns including first and second runs extendinggenerally longitudinally on first and second sides of said major axis,respectively,

d. one of said first and second runs having first conductor portionmeans positioned sufficiently close to said major axis of said layer topermit the exercise of effective electromagnetic influence when currentis passing therethrough on said planar path adjacent the major axis butnot on the outer edges of said planar path,

e. another of said first and second runs having second conductor portionmeans spaced from the major axis of said layer to permit the exercise ofeffective electromagnetic influence when current is passing therethroughon at least one outside edge of said planar path but not on that part ofsaid planar path adjacent the major axis of said layer,

f. said first and second conductor portion means of said first andsecond runs being connected by third conductor portion means extendinggenerally obliquely across said layer with respect to said major axis topermit the exercise of effective electromagnetic influence in responseto current flow therethrough generally obliquely across said planar pathbetween the outside edges of said planar path, whereby effectivemagnetic influence is shifted transversely across a planar surfacemoving through said planar path to effectively heat the entire planarsurface.

2. An inductive heating coil as defined in claim 1 which furtherincludes a. said plurality of turns of said conductor followingsubstantially the same configuration in said layer, and

b. a split, single turn metallic sheath secondary extending around andin the same configuration as said turns of said conductor and on theside of said layer to be located adjacent said path,

c. said single turn secondary being electrically and mechanicallysecured to one of said plurality of turns. v

3. An inductive heating coil for connection to a source of inductiveheating current for heating a planar surface of a conductive material,comprising a. a conductor shaped into a plurality of elongated turnsforming a layer-like inductive heating coil;

b. said elongated layer-like heating coil having longitudinallyextending first and second runs of said turns, at least one of said runsbeing disposed in inductive heating relationship in a plane adjacent andsubstantially parallel to a planar path defined by movement of a planarsurface to be heated, and means for connecting said first and secondruns to enable flow of inductive heating current therethrough;

c. said; first and second runs having first conductor portion meanspositioned in said plane to permit electromagnetic inductive heating ofthe edges of said planar path, but not the part of said planar pathbetween the edges thereof;

d. said first and second runs having second conductor portion meanspositioned in said plane to permit electromagnetic inductive heatingacross the planar path but not at both edges of the path at the sametime;

e. said second conductor portion means extending obliquely with respectto the planar path across the plane parallel to the planar path so thatelectromagnetic inductive heating is permitted across the entire widthof said planar path between said edges;

f. said first and said second conductor portion means being connected toenable flow of inductive heating current therethrough and in said firstand second runs, thereby enabling the heating of the entire surface ofsaid planar surface passed along said planar path.

4. An inductive heating coil as defined in claim 3 in which a. saidfirst run of said coil comprises one part starting adjacent one outsideedge of said planar path and includes at least one excursion obliquelytoward and then away from said major axis, and a second part whichextends linearly adjacent said one outside edge, and in which saidsecond run of said coil comprises one part opposite said one part ofsaid first run which extends linearly adjacent the other outside edge ofsaid planar path, and a second part opposite said second part of saidfirst run starting adjacent said other outside edge and includes atleast one excursion obliquely toward and then away from said ma or axis.

. 5. An inductive heating coil as defined in claim 4 in which said firstand second runs each further include linearly extending sectionsadjacent said major axis connecting the inner reaches of each excursion.

6. An inductive heating coil as defined in claim 3 in which said firstand second runs of said coil each start adjacent their respectiveoutside edge of said path and continue obliquely inwardly toward eachother and said major axis until the major axis is-under efi'ectivemagnetic influence when current flows through said runs.

7. An inductive heating coil as defined in claim 6 in which saidfirstand second runs continue from their innermost position obliquelyoutwardly away from each other and said major axis returning to aposition adjacent their respective outer edge of said path.

8. An inductive heating-coil as defined in claim 3 in which-said firstand second runs of said coil each start adjacent said major axis andcontinue obliquely outwardly away from each other to a position adjacenttheir respective outer edge of said path.

9. An inductive heating coil as defined in claim 8 in which said firstand second runs continue from their outermost position obliquelyinwardly toward each other and said major axis until the major axis isunder effective. magnetic influence when current flows through saidruns.

10. An inductive heating coil as defined in claim 3 in which I a. one ofsaid first and second runs of said coil starts adjacent said major axisand continues obliquely outwardly to a position adjacent its respectiveouter edge of said path, and in which b. the other of said first andsecond runs of said coil starts adjacent its respective outer edge ofsaid path and continues obliquely inwardly to a position adjacentsaidmajor axis.

11. Apparatus for sealing wide-mouth containers by bonding across and tothe containerfinish a closure member, comprising.

a. means for conveying a container assembly having a thermoplasticbonding material held in place between a closure member and thecontainer finish, and a substantially planar metallic susceptor disposedin conductive heating relationship with the bonding material, in adirection so that the movement of said planar susceptor defines asubstantially planar path;

b. a conductor formed into an elongated turn as an inductive heatingcoil, said coil having means for inductive heating of the edges of saidplanar path, 6

but not the part of said planar path between the edges thereof;

c. said turn also having second conductor portion means positioned insaid plane topermit electromagnetic inductive heating across the planarpath but not at the edges of said planar path;

f. said second conductor portion means extending obliquely with respectto the planar path across the plane parallel to the planar path so thatelectromagnetic inductive heating is permitted across the entire widthof said planar path between said edges; 7

g. said first and said second conductor portion means being connected toenable flow of inductive heating current therethrough and in said firstand second runs, thereby enabling the heating of the entire surface ofsaid planar surface passed along said planar path.

12. Apparatus as defined in claim 11 in which a. said first run of saidcoil comprises one part starting adjacent one outside edge of saidplanar path and includes at least one excursion obliquely toward andthen away from said major axis, and a second part which extends linearlyadjacent said one outside edge, and in which b. said second run of saidcoil comprises one part opposite said one part of said first run whichextends linearly adjacent the other outside edge of said planar path,and a second part opposite said second partof said first run startingadjacent said other outside edge and includes at least one excursionobliquely toward and then away from said major axis.

13. Apparatus as defined in claim 12 in which said first and second runseach further include linearly extending sections adjacent said majoraxis connecting the inner reaches of each excursion.

14. Apparatus as defined in claim 11 in which said first and second runsof said coil each start adjacent their respective outside edge of saidpath and continue obliquely inwardly toward each other and said majoraxis until the major axis is under effective magnetic influence whencurrent flows through said runs.

15. Apparatus as defined in claim 14 in which said first and second runscontinue from their innermost position obliquely outwardly away fromeach other and said major axis returning to a position adjacent theirrespective outer edge of said path.

16. Apparatus as defined in claim 11 in which said first and second runsof said coil each start adjacent said major axis and continue obliquelyoutwardly away from each other to a position adjacent their respectiveouter edge of said path.

17. Apparatus as defined in claim 16 in which said first and second runscontinue from their outermost position obliquely inwardly toward eachother and said major axis until the major axis is under effectivemagnetic influence when current flows through said runs.

18. Apparatus as defined in claim 11 in which a. one of said first andsecond runs of said coil starts adjacent said major axis and continuesobliquely outwardly to a position adjacent its respective outer edge ofsaid path, and in which b. the other of said first and second runs ofsaid coil starts adjacent its respective outer edge of said path andcontinues obliquely inwardly to a position adjacent said major axis.

19. Apparatus as defined in claim 11 in which b. current supplying meansfor supplying a magnitude and frequency of inductive heating currentthat cooperates with the number of turns in said coil to activate thebonding material by heating said susceptor without damaging thelaminated disc or the container finish.

1. An inductive heating coil for connection to a source of inductiveheating current for heating a planar surface of a conductive materialcomprising a. a conductor shaped into a plurality of elongated turnsforming a layer coil, one side of said layer defining a plane fordisposition in inductive heating relationship adjacent and substantiallyparallel to a planar path defined by movement of a planar surface in alinear direction, b. the elongated turns of said layer having a majoraxis for disposition substantially parallel to the linear direction ofmovement of the planar surface in defining said planar path, c. saidelongated turns including first and second runs extending generallylongitudinally on first and second sides of said major axis,respectively, d. one of said first and second runs having firstconductor portion means positioned sufficiently close to said major axisof said layer to permit the exercise of effective electromagneticinfluence when current is passing therethrough on said planar pathadjacent the major axis but not on the outer edges of said planar path,e. another of said first and second runs having second conductor portionmeans spaced from the major axis of said layer to permit the exercise ofeffective electromagnetic influence when current is passing therethroughon at least one outside edge of said planar path but not on that part ofsaid planar path adjacent the major axis of said layer, f. said firstand second conductor portion means of said first and second runs beingconnected by third conductor portion means extending generally obliquelyacross said layer with respect to said major axis to permit the exerciseof effective electromagnetic influence in response to current flowtherethrough generally obliquely across said planar path between theoutside edges of said planar path, whereby effective magnetic influenceis shifted transversely across a planar surface moving through saidplanar path to effectively heat the entire planar surface.
 2. Aninductive heating coil as defined in claim 1 which further includes a.said plurality of turns of said conductor following substantially thesame configuration in said layer, and b. a split, single turn metallicsheath secondary extending around and in the same configuration as saidturns of said conductor and on the side of said layer to be locatedadjacent said paTh, c. said single turn secondary being electrically andmechanically secured to one of said plurality of turns.
 3. An inductiveheating coil for connection to a source of inductive heating current forheating a planar surface of a conductive material, comprising a. aconductor shaped into a plurality of elongated turns forming alayer-like inductive heating coil; b. said elongated layer-like heatingcoil having longitudinally extending first and second runs of saidturns, at least one of said runs being disposed in inductive heatingrelationship in a plane adjacent and substantially parallel to a planarpath defined by movement of a planar surface to be heated, and means forconnecting said first and second runs to enable flow of inductiveheating current therethrough; c. said first and second runs having firstconductor portion means positioned in said plane to permitelectromagnetic inductive heating of the edges of said planar path, butnot the part of said planar path between the edges thereof; d. saidfirst and second runs having second conductor portion means positionedin said plane to permit electromagnetic inductive heating across theplanar path but not at both edges of the path at the same time; e. saidsecond conductor portion means extending obliquely with respect to theplanar path across the plane parallel to the planar path so thatelectromagnetic inductive heating is permitted across the entire widthof said planar path between said edges; f. said first and said secondconductor portion means being connected to enable flow of inductiveheating current therethrough and in said first and second runs, therebyenabling the heating of the entire surface of said planar surface passedalong said planar path.
 4. An inductive heating coil as defined in claim3 in which a. said first run of said coil comprises one part startingadjacent one outside edge of said planar path and includes at least oneexcursion obliquely toward and then away from said major axis, and asecond part which extends linearly adjacent said one outside edge, andin which b. said second run of said coil comprises one part oppositesaid one part of said first run which extends linearly adjacent theother outside edge of said planar path, and a second part opposite saidsecond part of said first run starting adjacent said other outside edgeand includes at least one excursion obliquely toward and then away fromsaid major axis.
 5. An inductive heating coil as defined in claim 4 inwhich said first and second runs each further include linearly extendingsections adjacent said major axis connecting the inner reaches of eachexcursion.
 6. An inductive heating coil as defined in claim 3 in whichsaid first and second runs of said coil each start adjacent theirrespective outside edge of said path and continue obliquely inwardlytoward each other and said major axis until the major axis is undereffective magnetic influence when current flows through said runs.
 7. Aninductive heating coil as defined in claim 6 in which said first andsecond runs continue from their innermost position obliquely outwardlyaway from each other and said major axis returning to a positionadjacent their respective outer edge of said path.
 8. An inductiveheating coil as defined in claim 3 in which said first and second runsof said coil each start adjacent said major axis and continue obliquelyoutwardly away from each other to a position adjacent their respectiveouter edge of said path.
 9. An inductive heating coil as defined inclaim 8 in which said first and second runs continue from theiroutermost position obliquely inwardly toward each other and said majoraxis until the major axis is under effective magnetic influence whencurrent flows through said runs.
 10. An inductive heating coil asdefined in claim 3 in which a. one of said first and second runs of saidcoil starts adjacent said major axis and continues obliquely outwardlyto a Position adjacent its respective outer edge of said path, and inwhich b. the other of said first and second runs of said coil startsadjacent its respective outer edge of said path and continues obliquelyinwardly to a position adjacent said major axis.
 11. Apparatus forsealing wide-mouth containers by bonding across and to the containerfinish a closure member, comprising a. means for conveying a containerassembly having a thermoplastic bonding material held in place between aclosure member and the container finish, and a substantially planarmetallic susceptor disposed in conductive heating relationship with thebonding material, in a direction so that the movement of said planarsusceptor defines a substantially planar path; b. a conductor formedinto an elongated turn as an inductive heating coil, said coil havingmeans for connecting inductive heating current thereto; c. saidelongated heating coil having longitudinally extending first and secondruns, at least one of said runs being disposed in inductive heatingrelationship in a plane adjacent and substantially parallel to saidplanar path defined by movement of said planar surface to be heated, andmeans for connecting said first and second runs to enable flow ofinductive heating current therethrough; d. said turn having firstconductor portion means positioned in said plane to permitelectromagnetic inductive heating of the edges of said planar path, butnot the part of said planar path between the edges thereof; e. said turnalso having second conductor portion means positioned in said plane topermit electromagnetic inductive heating across the planar path but notat the edges of said planar path; f. said second conductor portion meansextending obliquely with respect to the planar path across the planeparallel to the planar path so that electromagnetic inductive heating ispermitted across the entire width of said planar path between saidedges; g. said first and said second conductor portion means beingconnected to enable flow of inductive heating current therethrough andin said first and second runs, thereby enabling the heating of theentire surface of said planar surface passed along said planar path. 12.Apparatus as defined in claim 11 in which a. said first run of said coilcomprises one part starting adjacent one outside edge of said planarpath and includes at least one excursion obliquely toward and then awayfrom said major axis, and a second part which extends linearly adjacentsaid one outside edge, and in which b. said second run of said coilcomprises one part opposite said one part of said first run whichextends linearly adjacent the other outside edge of said planar path,and a second part opposite said second part of said first run startingadjacent said other outside edge and includes at least one excursionobliquely toward and then away from said major axis.
 13. Apparatus asdefined in claim 12 in which said first and second runs each furtherinclude linearly extending sections adjacent said major axis connectingthe inner reaches of each excursion.
 14. Apparatus as defined in claim11 in which said first and second runs of said coil each start adjacenttheir respective outside edge of said path and continue obliquelyinwardly toward each other and said major axis until the major axis isunder effective magnetic influence when current flows through said runs.15. Apparatus as defined in claim 14 in which said first and second runscontinue from their innermost position obliquely outwardly away fromeach other and said major axis returning to a position adjacent theirrespective outer edge of said path.
 16. Apparatus as defined in claim 11in which said first and second runs of said coil each start adjacentsaid major axis and continue obliquely outwardly away from each other toa position adjacent their respective outer edge of said path. 17.Apparatus as defined in claim 16 in which said first and second runscontInue from their outermost position obliquely inwardly toward eachother and said major axis until the major axis is under effectivemagnetic influence when current flows through said runs.
 18. Apparatusas defined in claim 11 in which a. one of said first and second runs ofsaid coil starts adjacent said major axis and continues obliquelyoutwardly to a position adjacent its respective outer edge of said path,and in which b. the other of said first and second runs of said coilstarts adjacent its respective outer edge of said path and continuesobliquely inwardly to a position adjacent said major axis.
 19. Apparatusas defined in claim 11 in which a. the closure member is in the form ofa laminated disc coated with the thermoplastic bonding material at leaston its interface with the container finish, and which further includesmetallic foil as the susceptor as a laminate at least in the area of thedisc adjacent the thermoplastic bonding material, and which furtherincludes b. current supplying means for supplying a magnitude andfrequency of inductive heating current that cooperates with the numberof turns in said coil to activate the bonding material by heating saidsusceptor without damaging the laminated disc or the container finish.